For example, a light guide plate display device in the related art which is disclosed in PTL 1 includes a light guide plate and a trigonal prismatic prism. Light radiated from an end face to an inside of the light guide plate is output from a display face of the light guide plate in the prism. In this manner, the light guide plate display device displays a pattern. FIGS. 25 and 26 are diagrams which illustrate the light guide plate display device in the related art which is described in PTL 1.
The light guide plate display device described in PTL 1 includes light guide plate 12, four light source device groups 211a to 211d, 212a to 212d, 213a to 213d, and 214a to 214d which radiate light from different directions, respectively, toward end faces of light guide plate 12, and four prism groups 19a, 19b, 19c, and 19d. In FIG. 25, as prism groups 19a, 19b, 19c, and 19d, each one prism is illustrated, respectively; however, in practice, prism groups are formed by being provided with a plurality of prisms in the inside of light guide plate 12.
Prism group 19a is formed in a trigonal prismatic shape with inclined faces which incline to light guide plate 12, respectively, and a perpendicular face which is perpendicular to light guide plate 12, and the inclined face of prism group 19a is provided so as to face a radiation direction of light source devices 211a to 211d. Light input to the inclined face of prism group 19a is reflected in a display direction of light guide plate 12, and is visually recognized by an observer. On the other hand, since light input to the perpendicular face of prism group 19a penetrates the prism, the light is not visually recognized by an observer. Prism group 19a is disposed at an appropriate position in light guide plate 12, and pattern P21 is displayed when light source devices 211a to 211d are turned on.
Inclined faces of prism group 19b are provided so as to face radiation directions of light source devices 212a to 212d, inclined faces of prism group 19c are provided so as to face radiation directions of light source devices 213a to 213d, and inclined faces of prism group 19d are provided so as to face radiation directions of light source devices 214a to 214d. In this manner, the inclined faces of prism group 19b reflect light radiated from light source devices 212a to 212d, and pattern P22 is displayed, the inclined faces of prism group 19c reflect light radiated from light source devices 213a to 213d, and pattern P23 is displayed, and the inclined faces of prism group 19d reflect light radiated from light source devices 214a to 214d, and pattern P24 is displayed. As described above, by performing switching of ON or OFF of light source devices 211a to 211d, 212a to 212d, 213a to 213d, and 214a to 214d, it is possible to display patterns P21 to P24 of four types, and a combination thereof on light guide plate 12.